Optical coupling device and method for fabricating the same, and master used in fabricating optical coupling device and method for fabricating the same

ABSTRACT

An integrated type optical coupling device capable of easily accurately performing an optical arrangement between a narrow-pitch multi-channel optical waveguide and an optical fiber array and a master used in fabricating the same are provided. By forming a fixing projection between the optical fibers, the dynamic stability of the optical fiber array is increased and the optical arrangement between the optical waveguide and the optical fiber is easily accurately performed by hand. Accordingly, the cost required for the alignment is reduced and the alignment error due to the rolling of the optical fiber is not generated. In addition, the multi-step metal master is fabricated by using a photoresist film for X-ray exposure, and the narrow-pitch multi-channel optical coupling device is fabricated in a hot embossing method using the same, thereby the high-integrated device can be fabricated at a low price.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical coupling device and a masterused in fabricating the optical coupling device, more particular, to anintegrated type optical coupling device and a master used in fabricatingthe optical coupling device that an optical alignment between anarrow-pitch multi-channel optical waveguide and an optical fiber arraycan be easily accurately performed and the fabricating cost thereof canbe reduced.

2. Description of the Prior Art

Recently, as an information communication industry is developed, datatransmission using a communication network such as Internet is activelyincreased, thereby large scale, high speed, and high density of atransmission/exchange system for increasing the transmitting amount andthe transmitting speed of data has been demanded. According to thedemand, the research for integrating the channel to 40 channels greaterthan the existing 8 or 16 channels in a same area has been progressed.At this case, since the pitch between the channels is reduced from 250μm to 125 μm, it is difficult to fabricate the system. Accordingly, theimplement of the optical device which can easily integrate the channel,can increase optical coupling efficiency with the optical fiber, and canreduce the fabricating cost thereof is needed.

Generally, the optical coupling device for optically coupling with theoptical fiber and electrically or optically controlling an opticalsignal comprises modules formed with a plurality of V-shaped grooves formounting an optical fiber array, a waveguide element coupled between themodules and formed with a multi-channel optical waveguide, and acontrolling means for electrically or optically controlling the opticalsignal transmitted through the optical waveguide.

In the conventional optical coupling device having the above-mentionedstructure, the module and the waveguide element are separatelyfabricated and are coupled with each other. Accordingly, first, opticalcoupling loss can be generated due to the variation if a thermal ormechanical impact is applied thereto. Second, since the dynamicstability of the optical fiber is not secured due to the space of thelower portion when the optical fiber is aligned in the V-shaped groove,the length of the V-shaped groove must be relatively long, thereby it isdifficult to reduce the size of the structure. Also, third, an expensiveoptical fiber aligning device must be used in order to make a preciseoptical alignment between the optical waveguide and the optical fiberarray. Fourth, since the optical fiber is fixed by an adhesive to makethe active optical alignment with the waveguide element after theintensity of the transmitted light is checked by the channel, the timeand technical cost required for aligning the optical fiber array isproportionally increased as the number of the channels is increased.

On the other hand, a master (a metallic pattern) is used inmanufacturing the module mounted with the optical fiber and thewaveguide element. The multi-step master is fabricated by a patterningprocess using several masks each having a different exposed location.Accordingly, there is a merit that multi-step structure having adifferent height proportional to the exposed number is made, but themasks as same number as the exposed number must be fabricated, anaccurate location alignment of the mask is need in each of the exposingsteps, and it is difficult to accurately adjust the time for exposingthe photoresist film and the height of the fine structure.

As an alternative method, a method for fabricating a master, applyingthe photoresist film thereon, and performing the plating to implement afine structure having various heights on the same surface is suggested.In this method, since the photoresist film is formed on the master andthen is exposed by using the mask, a precise mask aligning technique isneeded, the mask fabricating processes as same number as the number ofthe steps of the mask must be repeatedly performed. Above all, since aprecise dimension control determines the precision of the master whichis finally fabricated in the master fabricating process, a precisemachining technique is needed. In addition, there is a problem that thefine structure fabricated previously is damaged when forming thephotoresist on the fabricated master.

SUMMARY OF THE INVENTION

Thus, the object of the present invention is to fabricate a multi-stepmetal master capable of increasing a dynamic stability of an opticalfiber array by using a photoresist film for X-rays exposure andperforming a precise optical alignment between a waveguide and a opticalfiber, and provide an optical coupling device capable of solving theabove-mentioned problem by fabricating a narrow-pitch multi-channeloptical device by a hot embossing process using the master and a masterused in fabricating the same.

The optical coupling device according to the present invention foraccomplishing the above-mentioned object comprises a substrate; and aclad formed on the substrate and having a convex portion protruded atthe middle portion thereof and concave portions located at both sides ofthe convex portion, wherein the convex portion having a plurality ofwaveguides formed thereon in a longitudinal direction and wherein theconcave portion having a plurality of optical fiber fixing groovesseparated from each other by fixing projections so that each of theoptical fiber fixing grooves is matched with each of waveguides.

The optical coupling device further comprises electrodes located on thewaveguides for controlling optical signals transmitted through thewaveguides, and the clad is composed of polymer.

The height h of the fixing projection is obtained by the next equation1: $\begin{matrix}{h \geq {R\left( {1 - \frac{1}{\sqrt{\left( \frac{F}{W} \right)^{2} + 1}}} \right)}} & (1)\end{matrix}$

Here, R is the radius of the optical fiber, F is the force applied tothe optical fiber from the outside, and W is the weight of the opticalfiber.

The method for fabricating an optical coupling device according topresent invention for accomplishing the above-mentioned object comprisesthe steps of forming a lower clad layer on a substrate; positioning ametal master on the lower clad layer and applying a heat thereto;pressing the master to the lower clad layer to mold a lower clad havinga convex portion protruded at the middle portion thereof and concaveportions located at both sides of the convex portion, wherein the convexportion has a plurality of waveguides formed thereon in a longitudinaldirection and wherein the concave portion has a plurality of opticalfiber fixing grooves separated from each other by fixing projections sothat each of the optical fiber fixing grooves is matched with each ofwaveguides; forming a core in the waveguide formed in the convex portionof the lower clad; forming an upper clad on the core; and formingelectrodes on the upper clad.

The heat is at least a transition temperature of glass, and, when thelower clad is molded, a hot embossing device is used.

The core is formed by the steps of applying polymer on the lower clad;positioning a mask formed with a pattern on the lower clad so that onlythe waveguide is exposed to ultraviolet rays and irradiating theultraviolet rays to harden the polymer of the exposed portion; andremoving the unhardened polymer to leave the polymer for the core in thewaveguide.

The master used in fabricating the optical coupling device according tothe present invention for accomplishing the above-mentioned object hasrectangular-shaped protrusions for forming the optical fiber fixinggroove formed on both sides of a flat plate, a plurality of grooves forforming the optical fiber fixing projection formed on therectangular-shaped protrusions, and a plurality of lines forming thewaveguide formed between the rectangular-shaped protrusions on the flatplate.

The method for fabricating a master used in fabricating the opticalcoupling device according to the present invention for accomplishing theabove-mentioned object comprises the steps of fabricating a structurehaving a convex portion protruded at the middle portion thereof byetching both sides of a substrate by a predetermined depth and concaveportions at both sides of the convex portion; applying a photoresistfilm on the structure and removing the photoresist film by apredetermined thickness so as to form a step in the surface thereof;exposing and developing the photoresist film so that a photoresist filmpattern for forming the waveguide is formed in the convex portion of thesubstrate and a photoresist film pattern for forming the optical fiberfixing projection is formed in the concave portion of the substrate;filling polymer in grooves between the photoresist film patterns forforming the waveguide; immersing the substrate in a plating bath toplate the concave portion with a metal, until the surface of thephotoresist film pattern of the convex portion; removing the polymerfilled in the groove between the photoresist film pattern for formingthe waveguide; immersing the substrate in the plating bath again toplate the photoresist film pattern of the convex portion and the platedmetal on the concave portion with a metal by a predetermined thickness;and removing the substrate.

The method for fabricating a master further comprises the step ofapplying a metal for the plating and an adhesive to the structure afterthe step of fabricating the structure, and the photoresist film is thephotoresist film for X-ray exposure, and the photoresist film is removedby a predetermined thickness in a laser ablation method.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS

FIG. 1 is a perspective view of an optical coupling device according tothe present invention.

FIG. 2 is a side view of FIG. 1.

FIG. 3 is a cross-sectional view illustrating the structuralcharacteristics of the optical coupling device according to the presentinvention.

FIGS. 4 a and 4 b are partially detail views showing an opticallyaligned example by using the optical coupling device according to thepresent invention.

FIGS. 5 a to 5 i are views illustrating a method used in fabricating theoptical coupling device according to the present invention.

FIG. 6 is a perspective view of a master for fabricating the opticalcoupling device according to the present invention.

FIGS. 7 a to 7 j are views illustrating a method for the master used infabricating the optical coupling device according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides an optical coupling device based on anarrow-pitch multi-channel optical fiber array and a master used infabricating the same. The optical coupling device is designed so thatthe dynamic stability of the optical fiber array is increased to improvethe optical coupling efficiency with the optical waveguide and themulti-step master is designed to be easily and precisely fabricated. Thepresent invention can efficiently reduce the fabricating cost byfabricating the optical coupling device by the hot embossing processusing the multi-step master.

In the present invention, in order to secure the dynamic stability ofthe optical fiber array, a fixing projection is formed in the opticalfiber aligning portion to prevent the rolling of the optical fiber.Accordingly, the optical alignment between the optical waveguide and theoptical fiber can be manually performed, thereby the cost required forthe alignment is reduced and the alignment error due to the rolling ofthe optical fiber is not generated.

Hereinafter, the embodiments of the present invention will be explainedwith reference to the accompanying drawings. However, the embodiment ofthe present invention can be changed into a various type, and it shouldbe not understood that the scope of the present invention is limit tothe following embodiments. The embodiments of the present invention areprovided in order to explain the present invention to those skilled inthe art. In drawings, the size and the thickness of the film or theregion are shown in an exaggerated shape or a different shape, forclearness.

FIG. 1 shows all the structure of the optical coupling device accordingto an embodiment of the present invention.

On a substrate 1, a clad 2 consisting of polymer layer and having aconvex portion at a middle portion thereof is formed. A plurality ofwaveguides 2 a are formed in the convex portion of the clad 2 in alongitudinal direction. A plurality of optical fiber fixing grooves 2 cseparated from each other by fixing projections 2 b are formed in theconcave portion so that each of the optical fiber fixing grooves 2 c ismatched with each of the waveguides 2 a. A clad 4 are formed on thewaveguide 2 a and electrodes 4 a are formed on the clad 4.

An optical fiber 3 is inserted into each of the optical fiber fixinggrooves 2 c to be matched with the waveguide 2 a. When an optical signalis transmitted from the core of the optical fiber 3 to the core of theopposite optical fiber 3 through the waveguide 2 a, an electrical signalis applied to the electrode 4 a formed on the clad 4 to electricallycontrol the progressed optical signal. This structure is, for example,adapted to the optical device such as an optical attenuator.

FIG. 2 is a side view of FIG. 1. In order to increase the channel numberto at least 40 while maintaining the same dimension as the prior art,the pitch between the optical fibers 3 must be decreased from 250 μm to125 μm. Considering the error of the diameter of the optical fiber, itis preferable that the pitch must be 127 μm. The horizontal and verticallength of the waveguide forming a single mode 2 a are 7.0 μm or lessfor, and the diameter of the core 3 a of the optical fiber for thesingle mode become 9.0 μm or less.

The optical coupling efficiency in the single mode is at a maximum whenthe core 3 a of the optical fiber is located in the center of theoptical waveguide 2 a. For this, the depth of the fixing groove 2 c isadjusted to 66 μm so that the core 3 a of the optical fiber is locatedin the center of the waveguide 2 a. Also, in order to preventhorizontally moving the core 3 a of the optical fiber due to the rollingof the optical fiber 3, rectangular fixing projections 2 b arerespectively formed between the optical fiber fixing grooves 2 c.

FIG. 3 is a detail illustrating the dynamic relationship between thefixing projection 2 b and the optical fiber 3, wherein H is the heightof the convex portion formed with the waveguide 2 a, d is the width andthe depth of the waveguide 2 a, and D is the distance (pitch) betweenthe waveguides 2 a. The height h of the fixing projection 2 b forpreventing the alignment error between the waveguide 2 a and the opticalfiber 3 generated due to the rolling of the optical fiber 3 when tiltingall the structure is expressed by the next equation 2. $\begin{matrix}{h \geq {R\left( {1 - \frac{1}{\sqrt{\left( \frac{F}{W} \right)^{2} + 1}}} \right)}} & (2)\end{matrix}$

Here, R is the radius of the optical fiber 3, F is the force applied tothe optical fiber 3 from the outside, and W is the weight of the opticalfiber 3.

For example, supposing that the minimum force F for rolling the opticalfiber 3 is equal to the weight W of the optical fiber 3 and the radius Rof the optical fiber 3 is 62.5 μm, the height h of the fixing projection2 b becomes about 18.3 μm.

FIGS. 4 a and 4 b illustrate the example of realizing the opticalalignment between the waveguide 2 a and the optical fiber 3 by using theoptical coupling device according to the present invention, wherein thecenter of the core 3 a of the optical fiber is accurately matched withthe waveguide 2 a, and the optical fiber 3 is fixed by the fixingprojection 2 b.

Next, the method for fabricating the optical coupling device accordingto the present invention will be explained with reference to FIGS. 5 ato 5 i. In this embodiment, for example, the optical attenuatorfabricating procedures will be described.

Referring to FIG. 5 a, a lower clad layer 12 consisting of the polymeris formed on a substrate 11.

Referring to FIG. 5 b, the substrate 11 formed with the lower clad layer12 is positioned in the lower end of a hot embossing device and amulti-step master 13 fabricated according to the present invention ispositioned in the upper end of the hot embossing device. And then, theheating treatment is performed at a transition temperature of a glass,for example, a temperature of 130° C. to 200° C. The multi-step master13 will be explained later.

Referring to FIG. 5 c, while maintaining the temperature, the master 13is pressed to the lower clad layer 12 in an appropriate pressure andthen is separated therefrom.

Referring to FIG. 5 d, when the master 13 is removed, the molding of thelower clad layer 12 is finished. The lower clad layer 12 is composed ofa convex portion at the middle portion thereof and concave portions atboth sides of the convex portion. A plurality of the waveguides 12 a areformed in the surface of the convex portion in the longitudinaldirection, and a plurality of optical fiber fixing grooves 12 cseparated from each other by fixing projections 12 b are formed in theconcave portion so that each of the optical fiber fixing grooves 12 c ismatched with each of the waveguides 12 a.

Referring to FIG. 5 e, polymer 14 is applied to the lower clad layer 12molded in FIG. 5 d. At this time, the material capable of being hardenedby ultraviolet rays is used as the polymer 14. The mask 15 formed with apattern 15 a is positioned on the lower clad layer 12 so that only thewaveguide 12 a is exposed to the ultraviolet rays and the ultravioletray are irradiated to harden the polymer 14 of the exposed portion. Atthis time, in order to prevent a slap generated in the core of thewaveguide 12 a from being formed, the mask 15 is pressed to the lowerclad layer 12 and the mask 15 having the material that is not adhered tothe hardened polymer 14 is used or the surface of the mask 15 ischemically treated.

Referring to FIG. 5 f, after the mask 15 is removed, the unhardenedpolymer 14 is cleaned to be removed, thereby the polymer 14 for the coreis embedded in only the waveguide 12 a.

Referring to FIG. 5 g, after polymer 16 to be used as an upper clad isapplied to all the structure, the mask 15 is positioned thereto, andthen the ultraviolet rays are irradiated to harden the polymer 16.

Referring to FIG. 5 h, after the mask 15 is removed, the unhardenedpolymer 16 is removed, and then an upper clad layer 16 is formed on thepolymer 14 for the core. At this time, the upper clad layer 16 can beapplied to both the polymer 14 for the core and the lower clad layer 12.

Referring to FIG. 5 i, a mask 17 for forming the electrode is positionedon the upper clad layer 16 and a metal is deposited to form theelectrode 18 of the optical attenuator.

Next, the optical fiber is inserted into the optical fiber fixing groove12 c, is aligned so that the core is matched with the core of thewaveguide 12 a, and is fixed by the polymer hardened by the ultravioletrays and having a refractive index similar to that of the core of theoptical fiber, thereby a optical attenuator or an optical device foroptically aligned with the optical waveguide by hand is fabricated.

Next, the master according to the present invention used in molding thelower clad layer 12 will be described with reference to FIG. 6.

The metal master 21 according to the present invention comprises a flatportion 22, a rectangular-shaped protrusion 23 formed on both sides ofthe flat portion 22 for forming the optical fiber fixing groove, aplurality of rectangular-shaped grooves 24 for forming the optical fiberfixing projection, and lines 25 protruded in a longitudinal directionfor forming the waveguide in the flat portion 22 between the protrusions23.

FIGS. 7 a to 7 j are views illustrating a method for the master used infabricating the optical coupling device according to the presentinvention.

Referring to FIG. 7 a, a structure composed of a convex portion A ofmiddle portion protruded by etching both sides of the substrate 31consisting of silicon Si by a predetermined depth and a concave portionB at both sides of the convex portion is fabricated. Next, an adhesive32 for improving the adhesive strength of the photoresist film for X-rayexposure is applied to the substrate 31.

Referring to FIG. 7 b, a photoresist film 33 for X-ray exposure isapplied to the substrate 31 applied with the adhesive 32.

Referring to FIG. 7 c, in order to easily fabricate the master andincrease the geometrical precision thereof, the photoresist film 33 ofthe concave portion B is removed by a predetermined thickness in a laserablation method. At this time, if necessary, the photoresist film 33 ofthe convex portion A can be removed by a predetermined thickness.

Referring to FIG. 7 d, a X-ray mask 34 formed with a waveguide pattern34 a and an optical fiber fixing groove pattern 34 b is positioned onthe photoresist film 33 and the structure is exposed by X-raysirradiated from a synchrotron.

Referring to FIG. 7 e, after the mask 34 is removed, the photoresistfilm 33 is developed, thereby the photoresist film pattern 33 a forforming the waveguide 12 a is formed in the convex portion, and thephotoresist film pattern 33 b for forming the optical fiber fixingprojection 12 b is formed in the concave portion.

Referring to FIG. 7 f, in order to prevent the difference between theplating speeds due to the difference between the heights of thestructure and easily fabricate the master, polymer 35 is filled in thegroove between the photoresist film patterns 33 a for forming thewaveguide 12 a which is relatively located in a high place. At thistime, instead of the polymer 35, the adhesive 32 can be used.

Referring to FIG. 7 g, the substrate 31 is immersed in a plating bath toplate the concave portion with a metal until the surface of thephotoresist pattern 33 a of the convex portion. At this time, thethickness of the metal 36 plated on the concave portion become theheight of the surface of the photoresist film pattern 33 a.

Referring to FIG. 7 h, the polymer 35 filled in the groove between thephotoresist film patterns 33 a for the waveguide 12 a is removed.

Referring to FIG. 7 i, the substrate 31 is immersed in a plating bathagain to plate the photoresist film pattern 33 a of the convex portionand the plated metal 36 of the concave portion with a metal by apredetermined thickness, thereby the master 36 a of the metal structureis fabricated.

Referring to FIG. 7 j, the master 36 a is separated from the substrate31.

As mentioned above, by forming the fixing projection between the opticalfibers, the present invention can increase the dynamic stability of theoptical fiber array and easily accurately perform the optical alignmentbetween the optical waveguide and the optical fiber by hand.Accordingly, the cost and time required for the alignment is reduced andthe alignment error due to the rolling of the optical fiber is notgenerated.

In addition, according to the present invention, the multi-step metalmaster is fabricated by using the photoresist film for X-ray exposureand the narrow-pitch multi-channel optical coupling device is fabricatedin the hot embossing method using the same, thereby the high-integrateddevice can be fabricated at a low price.

Although the present invention has been illustrated and described withrespect to exemplary embodiments thereof, the present invention shouldnot be understood as limited to the specific embodiment, and it shouldbe understood by those skilled in the art that the foregoing and variousother changes, omission and additions may be made therein and thereto,without departing from the spirit and scope of the present invention.

1. An optical coupling device, comprising: a substrate; and a cladformed on said substrate and having a protruding middle portion thereofand recessed portions located at both sides of said protruding portion,wherein said protruding portion having a plurality of waveguides formedthereon in a longitudinal direction; wherein said recessed portions havea plurality of optical fiber fixing grooves separated from each other byfixing projections so that each of the optical fiber fixing grooves ismatched with each of waveguides; and wherein the height h of said fixingprojection is obtained by the next equation:$h \geq {R\left( {1 - \frac{1}{\sqrt{\left( \frac{F}{W} \right)^{2} + 1}}} \right)}$wherein R is the radius of said the optical fiber, F is the forceapplied to said optical fiber from the outside, and W is the weight ofsaid optical fiber.
 2. The optical coupling device according to claim 1,further comprising electrodes located on said waveguides for controllingoptical signals transmitted through said waveguides.
 3. The opticalcoupling device according to claim 1, wherein said clad is composed ofpolymer.
 4. An optical coupling device, comprising: a substrate; and aclad formed on said substrate and having a protruding middle portionthereof and recessed portions located at both sides of said protrudingportion, wherein said protruding portion having a plurality ofwaveguides formed thereon in a longitudinal direction and wherein saidrecessed portions have a plurality of optical fiber fixing groovesseparated from each other by fixing projections so that each of theoptical fiber fixing grooves is matched with each of waveguides, saidfixing grooves and said fixing projection forming a rectangular recess;and wherein the height h of said fixing projection is obtained by thenext equation:$h \geq {R\left( {1 - \frac{1}{\sqrt{\left( \frac{F}{W} \right)^{2} + 1}}} \right)}$wherein R is the radius of said the optical fiber, F is the forceapplied to said optical fiber from the outside, and W is the weight ofsaid optical fiber.
 5. The optical coupling device according to claim 4,further comprising electrodes located on said waveguides for controllingoptical signals transmitted through said waveguides.
 6. The opticalcoupling device according to claim 4, wherein said clad is composed ofpolymer.